Arthur Leywin and Rosalia Eralidth (decided to change it to something else) became friends after he saved her from some bandits that were planning to sell her. He killed the bandits saved her and took her safely to her home town.
Although there is one thing different about Rosalia even though she's an elf her personality and powers are one of a demon(nezuko for example). She doesn't talk much like her sister but when she's with Arthur she becomes a lot more talkative. It was also because she was his fated half.
Her abilities are like John Doe from Unordinary. So she will have Ice, Plant and Aura Manipulation.
P.S:Updates to this book will be very slow.